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| hypercomplex cell |
neuron in the visual cortex that responds to presence of a line segment with a particular orientation that ends at a particular point within the receptive field
higher abstract level of information |
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jannalam Wed, 24 Mar 2010 00:31:21 GMT |
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| complex cell |
neuron in the visual cortex that responds to presence of line segment with a particular orientation located within its receptive field, esp. when the line moves perpendicularly to its orientation |
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jannalam Wed, 24 Mar 2010 00:31:21 GMT |
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| simple cell |
an orientation-sensitive neuron in the striate cortex whose receptive field is organized in an opponent fashion |
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jannalam Wed, 24 Mar 2010 00:31:21 GMT |
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| patient with agnosia from ventral stream damage (effect on perception of spatial location?) |
patient cannot tell which object is bigger, but CAN adjust fingers properly to pick them up |
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jannalam Tue, 23 Mar 2010 23:46:17 GMT |
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| damage to dorsal stream for perception of spatial location? |
person can tell which object is bigger, but trouble adjusting finger width to pick them up |
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jannalam Tue, 23 Mar 2010 23:46:17 GMT |
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| perception of spatial location |
parietal lobe "where" pathway: more of a "how pathway"?
-guiding movements base don visual information:
-saccades of eyes
-reaching; grasping |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| vestibulo-ocular reflex |
keeps eyes fixed on one point while head moves: brain stem
componensates for eye movements: a region at junction of temporal and parietal CTX, with vestibular systme input |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| akinetopsia |
inability to see movement - world is in snapshots; caused by damage to area V5 (MST) |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| TMS to V5 region? |
subjects can't tell which stimulus on a computer screen is moving; damage to this region is called AKINETOPSIA |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| optic flow |
in MST area: complex motion of points in visual field caused by relative movement b/w observer and environment; provides info about relative distance of objects from the observer and of the relative direction of movement |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| V5 or medial temporal (MT): |
this region responds to velocity and direction of movement - gets input from V1 and superior colliculus
-fast input; thick, heavily myelinated axons
-humans - V5 located in lateral occiptal cortex (not temporal) |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| MST (medial superior temporal) |
these neurons respond to radial, circular, spiral movement
important function of this region is: optic flow
-some compensation for eye movements
-which direction am I heading? |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| perception of movement - region(s) that respond to movement? |
-V5 or medial temporal (MT)
-MST (medial superior temporal) |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| parahippocampal place area (PPA) |
involved in perception of particular places (scenes and backgrounds) |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| extrastriate body area (EBA) |
invovled in perception of the human body and body parts other than faces...silhouettes stick figures, etc.
-when TMS (transmagnetic stimulation) used to disrupt EBA--> impaired ability to recognize body parts, but not face parts or motorcycles |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| fusiform face area (FFA) |
located in the inferior temporal lobe; involved in perception of faces and other complex objects that require expertise to recognize |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| prosopagnosia |
inability to recognize particular people by the sight of their face -
they can tell something is a face, see and describe features of the face, but can't recognize |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| lateral occipital complex (LOC) |
a region of the extrastriate cortex, involved in perception of objects other than people's bodies and faces (wide variety of objects and shapes) |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| perception of form |
involves ventral stream/inferior temporal cortex - for perception of whole 3D objects and backgrounds
-receptive fields of neurons in this area (TEO) are large - as entire half of visual field |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| visual agnosia |
inability to visually recognize and name a particular category of objects
deficits in visual perception in the absence of blindness; caused by brain damage |
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jannalam Tue, 23 Mar 2010 23:46:16 GMT |
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| cerebral achromatopsia |
inability to discriminate among different hues; caused by damage to area V8 of the visual association cortex. damage to central stream, magnocellular system intact |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| neurons in V4 |
this area seems to be invovled in the analysis of form as well as color - the color-sensitive neurons had rather unusual secondary receptive field: large region surrounding the primary field. |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| color constancy |
the relatively constant appearance of the colors of objects viewed under varying light conditions |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| info that the koniocellular system provides? |
Color: blue-yellow
Low sensitivity to contrast
Low spatial resolution
Slow temporal resolution
Ventral stream |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| info that parvocellular system provides? |
Color: red-green
Low sensitivity to contrast
High spatial resolution (ability to detect details)
Slow sustained response temporal resolution
Ventral stream |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| information that magnocellular system provides? |
Color: No
Sensitive to contrast: high
Spatial resolution: LOW (detect very fine details)
Temporal resolution: fast (transient response)
dorsal and ventral streams |
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jannalam Thu, 25 Mar 2010 11:29:38 GMT |
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| posterior parietal cortex |
highest level of dorsal stream of visual association cortex; involved in the perception of movement and spatial location |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| inferior temporal cortex |
highest level of ventral stream of visual association cortex; involved in perception of objects, including people's bodies and faces |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| ventral stream |
a system of interconnected regions of visual cortex involved in the perception of form, beginning with the striate cortex and ending with the inferior temporal cortex.
WHAT the object is; what color? |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| dorsal stream |
a system of interconnected regions of visual cortex invovled in the perception of spatial location, beginning with the striate cortex and ending with the posterior parietal cortex.
WHERE in space the object is; what direction of movement? |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| extrastriate cortex |
region of visual association cortex that surrounds the striate cortex; receives fibers from the striate cortex and from the superior colliculi and projects to the inferior temporal cortex |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| Visual association cortex |
Role is to combine individual modules from perceived objects and entire visual scenes.
hierarchy of info flow.
direction of info flow tends to be up the hierarchy ('bottom-up" processing)
Also some info travels down the hierarchy ("top-down" processing...V1->LGN) |
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jannalam Tue, 23 Mar 2010 21:50:47 GMT |
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| modular organization of V1 |
there is a very organized way that the striate CTX is set up - so that there is a map of different neurons
-each module~ 150,000 neurons
-each module processes info from one small part of visual field
-2 CO (cytochrome oxidase) blobs
-Neurons in CO blobs respond to color and low spatial frequencies; not orientation or movement; monocular |
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jannalam Mon, 22 Mar 2010 05:04:30 GMT |
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| binocular depth cues |
perceiving depth...
-stereopsis - sense of depth we get from both of our eyes
-most striate CTX neurons respond to info from both eyes
-many respond to retinal disparity
-these neurons contribute to perception of depth |
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jannalam Mon, 22 Mar 2010 05:04:30 GMT |
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| monocular depth cues |
perceiving depth...
-relative size
-relative movement (i.e. driving in a cae - things moving slower in the distance are farther away)
-color/detail (atmospheric haze; less detailed, dimmer things are farther away) |
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jannalam Mon, 22 Mar 2010 04:59:01 GMT |
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| spatial frequencies |
instead of detecting lines and edges, it is now thought that V1 neurons are responding to spatial frequencies. any visual pattern can be decomposed mathematically into several different sine waves (Fourier analysis) |
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jannalam Mon, 22 Mar 2010 04:59:01 GMT |
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| higher-level feature detectors |
simple, complex, and hypercomplex neurons; each level is integrating input from many neurons on the previous level |
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jannalam Mon, 22 Mar 2010 04:59:01 GMT |
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| feature detectors |
cells in the striate cortex selectively respond to particular features in the visual field; e.g. orientation |
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jannalam Mon, 22 Mar 2010 04:59:01 GMT |
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| striate cortex |
aka primary visual cortex aka V1
6 layers of neurons
"map" of left visual field on right V1, vice versa
Distorted map: 25% corresponds to fovea of retina
Feature detector neurons - fire more when they see certain types of lines/movemnet |
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jannalam Mon, 22 Mar 2010 04:43:49 GMT |
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| color constancy |
colors looks the same to us under different lighting conditions; cortex compares information from different parts of the retina to determine the color you perceive. It's not all in the retina! |
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jannalam Mon, 22 Mar 2010 04:43:49 GMT |
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| opponent color theory |
we have 2 types of receptors, red-green and blue-yellow. we perceive yellow as absence of blue stimulation, etc. |
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jannalam Mon, 22 Mar 2010 04:43:49 GMT |
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| Trichromatic theory |
we have 3 types of color receptors, each sensitive to one hue; other colors formed by blending |
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jannalam Mon, 22 Mar 2010 04:43:49 GMT |
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| "center-surround" receptor fields |
help us detect edges
color of squares look lighter up against the darker square - on edges - center surround organization emphasizes illuminiation - higher rate of firing on edges -- look lighter on edge |
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jannalam Mon, 22 Mar 2010 01:31:22 GMT |
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| "OFF" cells |
light in center-->decreased firing; light in surround-->increased firing |
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jannalam Sat, 20 Mar 2010 05:41:22 GMT |
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| "ON" cells |
light in center of field --> increased firing; light in surround-->decreased firing |
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jannalam Sat, 20 Mar 2010 05:41:22 GMT |
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| receptive field of a cell = |
portion of the visual field that that cell responds to |
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jannalam Sat, 20 Mar 2010 05:41:22 GMT |
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| the "non-conscious" visual pathway preserved in blindsight... |
axons from retinal ganglion cells that terminate in the superior colliculus in the brainstem |
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jannalam Sat, 20 Mar 2010 05:41:22 GMT |
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| 6 layers of LGN |
Parvocellular and magnocellular layers with koniocellular sub-layers in between.
Parvo and Konio - input from color-responsive retinal ganglion cells
LGN layers 2,3, 5 - from ipsilaterla eye
1, 4, 6 - from contralateral eye |
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jannalam Fri, 19 Mar 2010 16:47:38 GMT |
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| striate cortex |
where LGN neurons' axons terminate (aka primary visual cortex; V1) |
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jannalam Fri, 19 Mar 2010 16:47:38 GMT |
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| lateral geniculate nucleus of the thalamus (LGN) |
where axons from all ganglion cells gathered into the optic nerve or crossed over to other side of optic chiasm terminate; LGN neurons' axons terminate in the striate cortex |
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jannalam Fri, 19 Mar 2010 16:47:38 GMT |
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| How do photoreceptors work in information transmission in the retina? |
Light exposure--> Rhodopsin breaks down into opsin and retinal photopigments; hyperpolarization of photoreceptor membrane-->less neurotransmitter (inhibitory effects on bipolar cells) released; Light-->disinhibition of bipolar cells.
Bipolar cells excite ganglion cells--increase their rate of firing. |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| 3 layers in the retina |
photoreceptors (info in)
bipolar cells
ganglion cells (info out to brain)
also there are horizontal cells; amacrine cells |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| optic disk |
place where optic nerve exits the retina; we have a blind spot - where the optic disk is, the brain "fills in" that missing portion of the visual field |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| rods |
120 mil.
Black and white, greater sensitivity (respond to lower levels of light) |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| cones |
5 mil.
Color vision, higher acuity |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| fovea |
The central part of retina, has the highest density of cones = high acuity. |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| retina |
contains photoreceptors |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| smooth pursuit movements |
we can't make smooth movements unless following somehting. following object vs. vestibulo-ocular reflex |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| saccadic |
fast movements of the eye |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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| vergence |
movement of eye to focus |
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jannalam Fri, 19 Mar 2010 15:42:16 GMT |
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